[Hallicrafters] Re: Hallicrafters Digest, Vol 9, Issue 26 (Dummy Antenna)

[David C. Hallam]

Just for everyone's information in case you don't know;  The RMA dummy
antenna described by Jim is the same as the SM-35/URM-25 antenna simulator
as furnished with the URM-25D signal generator.

73
David C. Hallam
KC2JD

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Wormchile at aol.com
Sent: Monday, October 25, 2004 6:39 PM
To: hallicrafters at mailman.qth.net
Cc: Wormchile at aol.com
Subject: [Hallicrafters] Re: Hallicrafters Digest, Vol 9,Issue 26 (Dummy
Antenna)


The following discussion should answer some of the recent questions
concerning dummy antennas. In my library is a copy of Sams Postwar
Communications
Receiver Manual, CR1, publication date unknown but approximately  around
1950.
Included are Photofact sheets, containing schematics, parts  lists and
alignment
instructions, for the following Hallicrafters models: S-38,  S-40, S-40A,
S-41G, S-41W, S-47, S-51, S-52, S-53, SX-42 and SX-43.

 The RF and IF alignment instructions all contain a column describing  the
dummy antenna to be used during alignment. In most cases none is used for IF
alignment. However, in many cases a dummy antenna is required to properly
align
the RF sections. The exact configuration of the dummy antenna varies across
the  product line. In many cases it takes the form of a 300, 330 or 390 Ohm
carbon  resistor connected between the signal generator and the antenna
input. At
other  times an RMA dummy antenna is specified, described as: a 200 pF
capacitor in  series with a 20 microH choke, with the choke shunted with a
400 pF
capacitor in  series with a 400 Ohm carbon resistor. Above 2 MHz this
antenna
has a fairly  constant impedance of  390- 400 Ohms.

If anyone is interested, I will be happy to make Xerox copies of  any of the
above mentioned Photofact sets. The finished product should  be far superior
to anything downloaded from BAMA. I also used Excel to do an  impedance vs.
frequency analysis for the RMA dummy antenna. I will be happy to  email a
copy to
anyone who is interested.

Hope this clears up some of the fog.

73

Jim Mandelik, KD8AKJ


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